In 1839, the Irish physician William B. O'Shaughnessy carried out some of the earliest work introducing cannabis's medical properties to Europe, after observing its therapeutic use during his time working in India. His research opened the door for cannabis to be gradually incorporated into Western pharmacopeias.

Harry J. Anslinger spent three decades at the head of the U.S. Federal Bureau of Narcotics (FBN) and was the driving force behind the Marihuana Tax Act of 1937, which federalized cannabis prohibition in the country. In the early days of his tenure at the FBN, Anslinger paid little attention to cannabis — but once Prohibition (of alcohol) ended, his agency was left with little work to justify its existence, and he risked losing his position of influence. That's when he turned his attention to cannabis.

Anslinger went so far as to claim that Black and Latino people were the primary users of marihuana, and that it made them "forget their place" in American society. He voiced concern that allowing marihuana use among Black Americans could lead to consequences he described in openly racist terms regarding their behavior toward white women. These historically documented statements are today among the most frequently cited examples of how cannabis prohibition was born entangled with explicit racial prejudice, not public health evidence.

Reefer Madness was a film funded in 1936 by a group of churches and directed by Louis J. Gasnier, conceived as a morality lesson to show parents the supposed dangers of cannabis use. The plot depicted high-school students who, after smoking marihuana, turned violent to the point of killing their own parents. The film flopped commercially on release and was largely forgotten — until, decades later, it resurfaced as a cult classic on college circuits, precisely because of how absurd and over-the-top its claims were, ironically turning it into a cultural symbol of the pro-legalization counter-movement.

Historians specializing in the subject have strongly challenged how well the evidence for this theory actually holds up, pointing out that there is no direct documentation linking these companies to the drafting of the Marihuana Tax Act, and that the explanation best supported by primary sources remains the combination of Anslinger's bureaucratic ambition, media sensationalism, and racial prejudice described in the sections above. This doesn't mean these industries' interests were irrelevant to the economic context of the era, but the available evidence does not support a deliberate, coordinated "conspiracy" in the sense the theory is usually presented.

In 1941, every mention of cannabis was removed from the United States Pharmacopeia, the official reference compendium of recognized medications. It was the final step of a process that had begun barely four years earlier: a substance that had been recognized as medicine for 90 years (since 1851) was struck from the official record after less than half a decade of political and media campaigning.

The Single Convention on Narcotic Drugs, signed on March 30, 1961, in New York, is the principal international treaty that still shapes the global legal framework for drug control today. Cannabis and its derivatives were placed in Schedules I and IV of the Convention — Schedule IV reserved specifically for substances considered to have "limited or no therapeutic benefit" and a high potential for abuse, the most restrictive category alongside heroin. It was this treaty that exported the American prohibitionist model, built on the foundations described in the previous sections, to nearly the entire planet — including Spain, which ratified the Convention (published in the BOE in 1966, later updated by the 1975 Protocol).

It's important to be rigorous here: at least three other former Nixon advisors have denied that Ehrlichman ever said this, and have suggested the journalist misread a remark made sarcastically. The quote is, therefore, widely cited and consistent with the documented effects of Nixon's policy (see section 12), but its literal authenticity remains a matter of historiographical debate, and a rigorous account should present it as such, not as settled fact.

The idea that cannabis acts as a "gateway" to harder drugs became popular in American public discourse during these same decades of prohibitionist campaigning, as an additional argument for prosecuting it on the same level as far more dangerous substances. Later scientific literature has repeatedly pointed out that the observed correlation between cannabis use and use of other substances is better explained by shared social factors (availability, environment, illegality pushing users into unregulated markets where different substances coexist) than by any pharmacological "gateway" mechanism per se — an important distinction that was rarely given the same media megaphone as the original theory.

Spain ratified the 1961 Single Convention under the Franco regime, folding the international prohibitionist framework into its domestic law. After the Transition to democracy, Spanish legislation evolved into a distinctive model that's still often misunderstood today: private use and home cultivation for personal consumption are not treated as criminal offenses (although public consumption can still draw administrative sanctions under the Citizen Security Law), while cultivation, possession with intent to traffic, and sale do constitute criminal offenses under Article 368 of the Penal Code — the same article that comes up in the ongoing debate over CBD and "cannabis light" covered in other articles in this series.

According to a 2020 report by the ACLU (American Civil Liberties Union), Black people in the United States were 3.64 times more likely to be arrested for cannabis possession than white people, despite comparable rates of use between the two groups — a figure nearly identical to that of an earlier 2013 report (3.73 times). In some individual states, the disparity was as high as six, eight, or nearly ten times. The same report documents more than 6.1 million arrests for cannabis possession over the decade studied, and notes that even in states that had already legalized cannabis, the racial disparity in arrests hadn't fully disappeared. These figures connect directly to the original motivations described in sections 2 through 4 of this article: nearly ninety years after the Marihuana Tax Act, the pattern of unequal law enforcement that Anslinger helped establish was still statistically measurable.

On December 2, 2020, the UN Commission on Narcotic Drugs (CND) voted, by a simple majority (27 in favor, 25 against, 1 abstention) of its 53 member states, to remove cannabis and cannabis resin from Schedule IV of the 1961 Single Convention — the category reserved for substances with no recognized therapeutic value. It was the first formal recognition, at the United Nations level, that the original 1961 classification did not reflect the available scientific evidence on cannabis's medicinal value. Drug policy analysts have noted, however, that this change corrects the classification without directly challenging the colonial and racial legacy of the original prohibitionist architecture described in sections 2 through 4 of this article.

This article reconstructs documented historical facts and quotes widely referenced across journalistic, academic, and legal sources. Where a claim is subject to historiographical debate (such as the quote attributed to Ehrlichman), that has been explicitly noted. The goal is to offer rigorous historical context, not a one-sided, oversimplified account.